The present invention relates to electrochemoluminescent systems. It concerns, more particularly, a detector and a method for analyzing substances by generating and detecting the electrogenerated chemoluminescence (ECL) or electrochemoluminescence.
Chemoluminescence is used for analyzing biochemical or biological substances. It allows, in particular, traces of micro-organisms, hormones, viruses, antibodies, amines or proteins to be measured.
Chemoluminescent analysis consists in marking the substance sought by means of a chemoluminescent agent, the detection and analysis of which are achieved by measuring the light transmitted when, having been placed in an excited state, it returns to its initial state.
The excited state allowing light transmission is the product of a chemical reaction between two particular substances. The present invention concerns, more particularly, systems using an electrochemical reaction, called electrochemoluminescent systems, wherein at least one of the reagents is electrochemically produced from a substance initially present in the solution.
Known electrochemoluminescent systems generally include a cell for generating and detecting the electrogenerated chemoluminescence, which includes at least a working electrode, means for supplying the electrode with electric power, a photodiode for detecting the light generated and means for measuring the signal provided by the photodiode.
These systems use a single or two working electrodes, as will be described hereinafter. In both cases, in order to perform reliable measurements, the photodiode must be placed as close as possible to the place where the electrochemoluminescent reaction takes place. All the stray light must also be taken into account in order to eliminate as far as possible systematic errors.
Such conditions are relatively difficult to satisfy with respect to easy to use, inexpensive miniaturized systems.
In order to meet these requirements, the publication by Smith et al. xe2x80x9cElectrochemiluminescence at microelectrodes for biosensingxe2x80x9d (SPIE vol. 2978, 1977, pages 64-68, XP-002056761) discloses a miniaturized electrochemoluminescent cell whose different components are assembled to form a very compact structure.
The object of the present invention is to take an additional step in making electrochemoluminescent detectors of very small dimensions, which are simple and practical to use, are of low cost and allow a wide range of applications.
More precisely, the invention concerns an electrochemoluminescent detector for analyzing a biochemical or biological substance, of the type including at least one cell for generating and detecting the electrogenerated chemoluminescence, which includes:
at least one working electrode made on a substrate;
electric power supply means connected to said electrode;
a photodiode for detecting the light generated by electrochemoluminescence; and
means for measuring the signal provided by the photodiode.
According to the present invention, this detector is principally characterized in that the photodiode is produced by being integrated in the substrate of the working electrode.
In an advantageous manner, the cell includes two interdigitated working electrodes one of which is used as the anode and the other as the cathode. The cathode is made of carbon and the anode of a material selected from among platinum, gold, carbon and transparent metal oxides. The distance between the cathode and the anode is less than 10 microns.
According to a preferred embodiment, the cell includes a passivation layer in which the electrodes are integrated, while leaving a portion of their top surface in contact with the exterior, and an intermediate layer of dielectric material, arranged between the electrode and the substrate.
Preferably, the detector according to the invention includes two identical measuring cells, such as described above, whose respective electrodes are provided on the same substrate and whose respective photodiodes are made by being integrated in said substrate The electrode of only one of the cells is connected to the power supply means, and the measuring means include means for determining the difference between the signals provided by the photodiodes of the two cells. In this embodiment, the passivation layer and the intermediate layer are common to both cells.
The object of the present invention is also achieved by a method according to which the substance to be analyzed is in an aqueous solution. In this case, the cathode is made of carbon, while the anode is made of a material selected from among platinum, gold, carbon and other materials known to those skilled in the art, in particular transparent metal oxides, the distance between the cathode and the anode being less than 10 microns.